The present invention relates to a sheet feeder having a sheet hopper and a sheet feed roller for delivering each one of the sheets stacked in the hopper to a predetermined location.
In a known sheet feeder used in a printer, the sheet in the uppermost position of a sheet stack in a sheet hopper is delivered in the specified feed direction by a sheet feed roller which is in contact with the uppermost sheet. A slanted surface is connected to the hopper, so that a leading edge of the delivered uppermost sheet hits the slanted surface. Therefore, the uppermost sheet is flexed or bent, so that the uppermost sheet can be separated from the subsequent sheet of the sheet stack, and can be delivered to a specified position such as a printing position outside the hopper. This conventional arrangement is disclosed in, for example, Japanese Laid-Open Patent Application KokaiNo. Hei 2-132018 corresponding to a U.S. Pat. No. 5,026,042.
According to the disclosed conventional device, the separability of the sheet from the remaining sheet stack and a type or kind of sheets that can be used are limited by the properties of the slanted surface, such as its slope and coefficient of friction. For instance, since a sheet having a low rigidity is difficult to separate, the slope of the slanted surface must be increased to provide sufficient flexion to the flexible sheet. However, if a sheet having high rigidity such as a postcard or an envelope, hits the large sloped slanted surface, there is the danger that excessively large resistance may be imparted upon the rigid sheet, and slipping rotation may occur in the sheet feed roller.
In order to avoid this drawback, a stop member may be provided at the slanted surface in an attempt to improve separation efficiency of the sheet having low rigidity. However, since the sheet feeder must install sheets of various width, it would be rather difficult to determine the position of the stop member. If the position of the stop member is improper, the stop member may produce a local resistance against the delivery of the sheet, which causes diagonal feeding of the sheet.